This invention has wide application in situations where a liquid is required to be dispensed in metered amounts at regular intervals from a container and in which it is critical that contamination from outside, whether particulate or bacterial in nature, be excluded. This is most frequently encountered in the context of the dispensing of medicines such as ophthalmic medicines but the utility of the invention extends to the protection of any liquid against particulate contamination. For ease of understanding, however, the invention will be described primarily in the context of the application that, as is presently anticipated, will be the most commercially attractive.
Many drugs, particularly those used in treatment of various eye disorders, are administered in drop form. The drops are intended to free-fall onto the eye surface, where they distribute across the exposed eye. Dosage of these ophthalmic drugs is often crucial: lower than prescribed levels can result in failure of the treatment and consequent progression of the disease, higher levels can result in untoward side effects that can also interfere with successful resolution.
Complicating the administration of these drugs is the fact that they are often required several times a day and thus, to be practical, must be applied by the patients themselves and not by medical personnel who are formally trained in drug delivery. Patient administration of such drugs has resulted in two serious problems which must be solved for these medications to be successfully used: container contamination and flow rate.